Boolean difference modifier creating artefacts
Option A subdivide all faces of a cube, select the middle edges then bevel them. Either extrude the large faces inwards, or erase them and use a Solidify Modifier. If the former don't forget to remove doubles.



Option B Just select all fates then use Inset > Individual Faces then *Extrude > Region (Vertex Normals).



Also works in icospheres. If self intersections are not a concern you can use a Solidify Modifier replacing the last extrude step.



Alternatively you can use a Wireframe modifier, for a slightly different geometry.